Thermal Micro Sensors for Pressure Measurements in the High, Fine and Rough Vacuum Ranges

In this work the development and technology of new MEMS Pirani gauges are described. The design is outlined in detail, in particular its optimization by using an analytical model formed to describe the thermal behavior of these sensor chips. Two types of thermal conductivity vacuum gauges were engineered. By combining both, one can cover a pressure range from 1E−06 Torr to 760 Torr. The fabrication process is outlined in detail and chip properties were precisely characterized. A dedicated measurement setup was engineered allowing automated measurement procedures for multiple probes at once. The sensors’ performance-characteristics were calculated by a thermal conductances based analytical model and by a corresponding FEM (finite element method) simulation. Both models are capable of simulating the thermal responses on pressure or temperature changes. The signal voltage and the signal-voltage drift due to ambient temperature fluctuations were calculated with very good agreement to the data gathered by measurement. Next, the sensor chips were utilized to realize a new method for measuring the thermal accommodation coefficient of thin film surfaces in a compact setup. Platinum and gold films were characterized in combination with nitrogen and air, each. Finally, an innovative combination of two sensor chips was created to achieve better high vacuum sensitivity. This concept was simulated and verified by experiments with very satisfying results, which indicate a huge improvement in sensitivity for the 1E−05 Torr decade.